Boiler Leaking Water Cause And How to Fix a Boiler Leak Guide

Boiler Leaking Water Cause And How to Fix a Boiler Leak Guide

Boiler leaking water – What to do if you have a boiler leak & how to fix it

worcester bosch boiler

Let’s state the obvious here – a leaking boiler is not a good sign! Despite being a relatively common issue, a water leak from a boiler is one that requires the urgent help of a Gas Safe registered engineer.

Broken boiler leaking? – Get a fixed price in just 20 seconds – Click here

Although there may be some things you can do to keep the boiler leak damage to a minimum while you wait for a qualified engineer such as putting a bucket underneath to catch the water, fixing a leaking boiler is not a DIY situation but it can be cheaper than what a new boiler cost!

Unfortunately, even new boiler installations are also prone to leaking as they settle, so it is not uncommon for this to occur and is easily rectified by contacting the engineer to fix the installation fault.

Protect your home and pocket from costly boiler breakdowns with our boiler cover plans here:

Get Boiler Cover

Keep your boiler running properly and efficiently – Book your annual service now:

Book a boiler service

Get an online fixed price in 20 seconds:

What kind of fuel does your boiler use?

Boiler leaks: Are they dangerous?

A boiler leaking water isn’t directly dangerous but requires immediate attention when left for too long. It can lead to other problems that are harder to handle such as a completely broken boiler that is not working as the water dripping from a leaky boiler can cause other issues such as rust and damaging electrical components or functions inside your boiler.

A boiler leaking gas is dangerous and you should call the gas emergency line on 0800 111 999.

Here’s what you need to do as soon as you notice your boiler leaking and everything you need to know when it comes to your leaking boiler.

Video: Find Out Why Your Boiler Is Leaking Water!

Discover the cause of your boiler’s water leak by looking into the common causes of this problem. Watch this helpful video guide to gain insights and discover how to deal with the issue.

Water dripping from boiler pipes at the bottom

If you can actually see the water dripping from your boiler at the bottom or from the boiler pipework, then it is likely that a seal has broken, you have corroded pipes, or there are loose joints. Therefore the only way to fix this is by turning your boiler and water off and fixing these issues, which can only be done by a qualified Gas Safe heating engineer.

If the drip is small then you could put a bucket underneath it and then arrange for a gas engineer to attend over the coming days to fix the issue. If the water dripping starts to speed up and become a fast leak then you would need to consider an emergency call out.

If you have recently had a new boiler installation, then make sure you contact the company that fit the boiler as this should be rectified right away.

What should I do if my combi boiler is leaking?

Boiler leaking water

If your combi boiler is leaking water you should locate all the leaks and use a bucket or container to stop the leak from damaging your floor and wipe up the water that had already spilt.

It may also be worth tightening the fitting to see if that stops or slows the leak from the combi boiler.

The next steps are to turn off the water supply and switch off the heating, and finally, it is important to contact a Gas Safe registered engineer to take care of the problem to get your combi boiler back up and running.

Can I fix a leaking boiler myself?

It’s a good idea to call in a qualified engineer to fix a leaking boiler in order to make sure it is properly repaired, as this issue can lead to more serious damage that is harder to fix.

If you are having some trouble getting a heating engineer over to you immediately then there are some short-term solutions to minimise the issue, however, do bear in mind that a DIY attempt should only be made on very small leaks.

In this instance, you could use a boiler leak sealant or sealer which is an additive that forms a boiler leak seal to stop or block the leakage.

This is a temporary solution as all it does is stops the leak from causing further damage to your home therefore it is important to consult an engineer even if you have successfully managed to keep the leak at bay, as it is necessary to find the root cause of the problem and resolve it.

Get an online fixed price in 20 seconds:

What kind of fuel does your boiler use?

Boiler Water Leak – The most common reasons boilers leak

Water leaks are the most common leaks due to the fact that over time the water repeatedly expanding can take its toll on old pipework, fixtures and fittings. What you do next however can affect how bad the problem is.

Although it is important to call a Gas Safe engineer as soon as possible to prevent further damage to your boiler, if your boiler is leaking water, it does not require urgent action in terms of your own personal safety as with oil and gas leaks.

However, it is important to turn the electricity off to avoid the risk of an electric short-circuit and to prevent any damage to your central heating system.


An obvious sign of your boiler leaking water would be water spillage but sometimes this may not always be the case as another sign is if your boiler stops working or cuts out because of low boiler pressure, and then loses pressure quickly even if you top it up.

Additionally, if you can see stains, mould, or dampness on the walls, ceilings, or woodwork then this is another clear sign of water leaking from your boiler.

Of the three types, water leaks are the most common across all varieties of boilers and there is usually a root cause that leads to a boiler leaking water.

This is why it is important to get in touch with a Gas-Safe engineer to take a look and resolve the problem properly, rather than relying on short-term fixes, such as a boiler leak sealant so let’s take a look at what may be causing your combi boiler to leak water.

Get an online fixed price in 20 seconds:

What kind of fuel does your boiler use?

Why is my boiler leaking water?

Boiler leaking water

There are several reasons why your boiler may be leaking water, such as high boiler pressure, broken seals, pipe corrosion, loose connections and incorrect or faulty installations.

It is important to call in a heating engineer to find the root cause and resolve the matter quickly to avoid further, long-lasting damage.

Here are some common reasons why your boiler may be leaking water.

High boiler pressure

High boiler pressure can push everyone to their boiling point, and your home boiler is no different! When your boiler’s pressure is too cry, the pressure release valve (PRV) will either let out the water causing a leak or some parts. internally may fail which in turn leads to a leak. Most boilers have a pressure gauge which should be around 1.5 bar and green, especially if you have a combi Boiler.

If the boiler pressure gauge is above the green bar, then your boiler is under pressure! Often, bleeding your radiator can help relieve the pressure in your boiler. Some boilers have a pressure release valve if there is too much pressure as a safety precaution

Corrosion of pipework

It is not unusual for pipes and hot water cylinders to corrode, become brittle and then deteriorate, eventually causing a leak. This is why regular servicing is so important – if one single part is corroded, it is relatively cheap to call in a Gas Safe Engineer to replace it.

However, if the corrosion is quite severe then it may be necessary to purchase a replacement boiler altogether. The more leaks you have can also be an indicator of how corroded your boiler is.

Faulty boiler installation

If you have water leaking from the pipes immediately under the boiler, the most likely cause is that some joints in the pipework have not been fitted correctly. Pipe fittings are the most likely cause especially if you have just installed a new boiler.

Nevertheless, this is no cause for panic and outrage, it is quite common for new boiler installation to have small leaks. All you need to do is contact your boiler installer to fix the leaks and correct the pipework.

Broken seals

Not to state the obvious here, once a seal breaks or becomes damaged, it does lead to water escaping which results in a leaking boiler. Seals are fitted around or on parts and joints within your boiler and if your boiler becomes corroded over time, it can cause the seals to become damaged too. Once this happens, the water that is pumped through the system then leaks through the seal and often at an alarmingly rapid rate.

So, if you have boiler leakage with quite a bit of water and if it is leaking quickly, then impaired seals may be the culprit. Although applying a bit of sealant may be a good short term solution to stop the flow of water leaking, you will need a Gas Safe Engineer to take a look and may need to replace your boiler.

Faulty heat exchanger

If your boiler is particularly old or of low quality, then it is not uncommon for the heat exchanger to stop working or crack. Unfortunately, the heat exchanger is the most expensive part to replace and to add to the wave of bad news, it is not easy to identify whether your heat exchanger is leaking yourself.

You will need to call in a Gas Safe Engineer to take a look at the problem and investigate whether your heat exchanger is the problem. In most cases, a failed heat exchanger is an indicator that it may be time to invest in a new boiler.

High temperature

This leak is definitely one to watch out for, as it could lead to scaling water coming out from your taps. Boilers usually include a temperature control valve (TCV) and this keeps an eye on the temperature of the water inside your boiler and prevents the water temperature from getting too high.

However, if the TVC is unable to regulate the temperature, it may lead to leaks coming from the temperature valve. This is the result of a fault with the temperature sensors and again, requires a professional investigation by a Gas Safe Engineer.

How is a leaking boiler dangerous?

Leaking boiler

Unlike a gas leak, a leaking boiler does not pose a threat to your wellbeing and therefore in that sense, may not be considered dangerous.

However, a leaking boiler can be a huge danger to your bank account! When left unattended, or if you try to use a temporary solution permanently, such as using a sealant then this could lead to bigger and more expensive problems.

Not only can a leaking boiler cause damage to your boiler, such as rusting but it can also impact your entire home too. It is best to not use your boiler while is it leaking and until you have repaired or replaced it, as the leaks could end up spilling onto other electrical parts and short-circuiting.

The leaks could also spread around your house, damaging your furniture, floors, and other belongings racking up a bill to repair your boiler and the damage done to your home.

Additionally, unless it is a new boiler being installed incorrectly, a leaking boiler is usually a dramatic way for your boiler to say goodbye. Although the issue can be solved, in most cases leaking boilers are an indicator that it may be time to look for a replacement.

Moreover, this does give you the opportunity to review the needs of your home and see if you can invest in more affordable boilers that suit your home’s needs better.

Get an online fixed price in 20 seconds:

What kind of fuel does your boiler use?

How do I stop my boiler from leaking?

As the saying goes, the best offence is a good defence.

There are some measures you can take to ensure the longevity and good health of your boiler to prevent your boiler from leaking and boiling over!

tools to fix leaking boiler

For example, here are some actions you can take to check up on your boiler.

Annual boiler servicing

Getting your boiler serviced regularly allows professionals to catch minor problems before they become major ones and stops issues from developing further, such as corrosion of components within your boiler. Additionally, it is a warranty requirement and your warranty will be invalid without regular or yearly servicing.

Chemical flushes

As mentioned, the heating system is the most expensive part to fix when something goes wrong there, so it is worth investing in the system or chemical flushes to cleanse your heating system and prevent the build-up of anything that would inhibit it from working properly.

Magnetic boiler filter

A magnetic filter fitted to your boiler and central heating system can help. These are magnets that work to collect any metallic debris from your heating system and it is important to make sure any new boilers are fitted with them.

Magnetic boiler filters help extend the life of your boiler by preventing blockages from the build-up of debris in your heating system as well as lowering the risk of a leaking boiler.

Get an online fixed price in 20 seconds:

What kind of fuel does your boiler use?

My boiler is leaking water do I need a new boiler?

Boilers that are leaking water don’t immediately require replacing. Boiler leaks can be fixed and usually pretty easily by a Gas Safe registered engineer, but always remember, If your boiler is relatively new, your boiler is likely to still be under warranty too so you would have to pay for anything anyway.

If your boiler was completely broken and under warranty, you would end up with a brand new one for free from the manufacturer. Most warranties or guarantees cover parts and labour too so you shouldn’t have to pay a penny.

Why is my boiler leaking water from underneath?

One of the most common places for boilers to leak is from underneath. This however doesn’t always pinpoint exactly where the water is coming from as the water may be dripping or running down from various places in the boiler.

Unless you can actually see the source or pipe that is leaking then it will be hard to actually diagnose the problem without taking off the boiler cover and looking inside. We strongly recommend that you don’t do this unless you are qualified.

What other types of boiler leaks are there?

Your boiler could be leaking gas, water or oil and here are some telltale signs to help you figure out what is going on with your boiler and what you will need to do!

Gas Leak

A gas leak is not particularly common as modern boilers, such as gas condensing boilers, have a sealed combustion chamber where they burn gas or oil and the fumes are released outside for your safety, preventing harmful gasses from getting into your home.

A boiler leaking gas is dangerous and you should call the gas emergency line on 0800 111 999.

However, things don’t always work as well as they are meant to, so it is important to keep an eye out for telltale signs of a gas leak.

gas safe register heating engineer

Signs that your boiler is leaking gas include black stains above or near the boiler, an unusual amount of condensation on your windows, and the flame that confirms your boiler is working, known as a pilot light, turning orange or yellow instead of blue.

Additionally, in most cases, you will be able to smell the gas leak unless your boiler is leaking carbon monoxide as it can often be odourless which makes this very dangerous, which is why it is a good idea to have a carbon monoxide detector installed in your home.

If your boiler is leaking gas, you may be feeling dizzy, sick, tired, or have headaches, so if you are concerned that your boiler is leaking gas, it is important to act fast – you will need to open all your windows and doors, do not light any naked flames, including cigarettes, and call the Gas Emergency Services for free.

In light of this, depending on how you feel, it may also be worth getting some medical advice just to ensure your safety and well-being.

Oil Leak

Similar to a gas leak, sealed combustion chambers should usually prevent this type of leak from happening in modern boilers and obvious signs of a boiler leaking oil are spot oil stains or pooling in addition to a stronger oil smell than usual.

cogs for inside leaking boiler

If you are concerned that your boiler is leaking oil you need to locate the oil tank and close the tap or valve and then open the windows therefore opening the windows is an important step as it prevents harmful fumes from building up.

When it comes to clearing and collecting the leaking oil, try to collect it and contain it in a tub or put putting down sand or earth however it is essential that you make sure it is safe first before doing so, and avoid washing the oil away.

Call a heating engineer as soon as possible to come and repair the oil leak, and be mindful of whether you or anyone else in your home is feeling sick or dizzy as you will need to leave the house instantly.

What are the error codes for a leaking boiler?

Error codes are codes displayed on your boiler that indicate specific problems with your boiler and heating system. This saves you the trouble of having to figure out what is going on with your boiler or even missing the problem already until it is too late and has become a major one!

Most modern boilers with display systems will often showcase error codes for a leaking boiler. Instead of having to sift through your manual, here are the likely error codes associated with leaking boilers for specific brands.

Boiler BrandBoiler leaking error codes
Worcester BoschA1, E9, CE207, HO7
VaillantF.22, F.24, F.13, F.73, S.41, S.53
IdealF1, L1, FD
Baxi117, 118, 125, E78, H.02 – 06

Please note, these are the specific brand models the above likely error codes relate to:

  1. Worcester Bosch: Worcester CDi Class, Worcester CDi Highflow, Worcester CDi Compact, Worcester Greenstar 25i, Worcester Greenstar 30i and all Worcester regular & Worcester system boilers
  2. Vaillant: Vaillant EcoMax Pro, Vaillant EcoTEC Pro, Vaillant EcoTEC Plus
  3. Ideal: Ideal Logic, Ideal Logic Plus, Ideal Mini, Ideal Vogue, Ideal Independent and Ideal Isar
  4. Baxi: all Baxi boiler models included

Hopefully, you now have the knowledge to know how to identify a leaking boiler – and if you ever wish to install a new boiler, Boiler Central is providing the ultimate boiler installation service for you!

Best boilers to replace old leaking boilers

If you have an old boiler on the other hand, it may be more economical to replace it. Here is a list of replacement boilers that are available now that are reliable, come with long warranties, and shouldn’t be leaking water any time soon:

How to keep your boiler from breaking down in the future:

Having your boiler serviced on a regular basis is the best way to avoid costly, inconvenient, and even dangerous boiler faults. In fact, you should have all gas appliances in your home safely checked and serviced by a Gas Safe registered engineer on an annual basis.

Matter of fact, we offer boiler cover with free annual boiler servicing, so instead of making a yearly appointment, you can rely on us to assist and check your boiler on a regular basis. If you don’t want to pay for expensive home emergency cover then this is another option.

Get an online fixed price in 20 seconds:

What kind of fuel does your boiler use?

Get a great price on a Which? Best Buy boiler online in minutes

  • Over 15,000 boilers installed
  • Rated excellent on Trustpilot
  • Fixed and final prices
  • No pushy salespeople
  • Next-day installation
  • 0% deposit interest-free finance
12-year warranty on Worcester Bosch & ViessmannGet a quote now >